Porous inorganic fine particles

ABSTRACT

The present invention provides an amorphous porous inorganic substance having small particle sizes and uniform pores, a process for synthesizing the same, and use of the same. The invention provides an amorphous porous inorganic substance having pores of a uniform pore diameter, which has an average particle size D L  of 10 to 400 nm as measured by a dynamic light scattering method and a specific surface area difference, S B -S L , between a conversion specific surface area S L  calculated from D L  and a nitrogen adsorption specific surface area S B  obtained by the BET method, of 250 m 2 /g or more. A process for synthesizing the same and use of the same are also disclosed.

TECHNICAL FIELD

This invention relates to a finely particulate amorphous porousinorganic substance and its sol; a process for synthesizing the same;use of the same; ink-jet recording media containing the same, which areused for inkjet printing or recording, such as papers, sheets, films,and fabrics; and a coating liquid used to produce the inkjet recordingmedia.

BACKGROUND ART

Technologies using fine inorganic particles attract attention not onlyfrom expectation for improved functions of electronic materials but alsofrom the standpoint of energy saving and environmental conservation.

Known fine inorganic particles, which are mostly produced by a vaporphase method or a liquid phase method, include oxides, such as Aerosiland colloidal silica, and metal particles, such as colloidal gold. Mostof them are solid particles with no pores inside. On the other hand,known amorphous porous inorganic substances include gels with poresbetween grains, such as silica gel and alumina gel, and amorphousactivated carbon, which are generally large particles.

Known amorphous porous inorganic fine particles include fine sphericalporous silica particles disclosed, e.g., in JP-B-4-70255, but such atechnique merely provides those having irregularly-shaped andsmall-diameter pores. Porous inorganic fine particles synthesized byusing a template include those disclosed in Chem. Lett., (2000), 1044,Stu. Sur. Sci. Catal., 129 (2000), 37, and JP-A-11-100208, but all ofthem are crystalline. Substances with a regular structure exhibitingcrystallinity are not always favorable for use as an adsorbent or acatalyst carrier on account of their shape selectivity. Further, therewas obtained a precipitate in each case, and a sol having fine particlesdispersed therein has not yet obtained. Examples of an amorphous porousinorganic substance obtained using a template include those disclosed inJP-A-2000-109312. However, the synthesis disclosed therein is carriedout by a precipitation method using a combination of a metal silicateand an inorganic acid, and hence the product has a large particle sizeand is not obtained in the form of sol.

Inkjet recording has been extending its use in wide fields because oflow noise, color recording capabilities, and high-speed recordingcapabilities. Since wood-free paper, etc. that are used in generalprinting are inferior in ink absorptivity, ink drying properties andimage quality such as resolution, improved dedicated papers have beenproposed to solve these inferiorities. Recording papers coated withvarious inorganic pigments including amorphous silica to have improvedink color developability or reproducibility have been disclosed (see,e.g., JP-A-55-51583 and JP-A-56-148585). However, along with recentprogress of the performances of inkjet printers, further improvementshave been demanded also on recording media and a satisfactoryperformance is not necessarily obtained merely with the above-describedtechnique. In particular, obtaining high image quality equal to silverhalide photographs involves increases of the ink ejection amount perunit area of a recording medium, which gives rise to insufficient inkabsorptivity and blurring problems. Further, transparency of an inkabsorbing layer has also been demanded for realizing high image qualityand color density comparable to silver halide photographs.

The present invention is to provide an amorphous porous inorganicsubstance having a small particle diameter and a uniform pore shape, asol thereof, and a synthesis process therefor.

Also, the present invention is to provide use of the substance,particularly an inkjet recording medium excellent in ink absorptivityand transparency, and a coating liquid for inkjet recording media.

DISCLOSURE OF THE INVENTION

The present invention provides the followings:

-   -   (1) A porous substance comprising inorganic particles which are        amorphous and have pores of a uniform diameter,    -   wherein said particles have an average particle size D_(L) of 10        to 400 nm as measured by a dynamic light scattering method, and    -   wherein said porous substance has a specific surface area        difference, S_(B)-S_(L), between a conversion specific surface        area S_(L) calculated from D_(L) and a nitrogen adsorption        specific surface area of the particles S_(B) obtained by the BET        method, of 250 m²/g or more.

(2) The porous substance set forth in item (1), wherein the pores havean average diameter of 6 nm or larger.

(3) The porous substance set forth in item (1) or (2), wherein theinorganic material is silicon oxide.

(4) The porous substance set forth in item (1) or (2), wherein theinorganic material contains silicon and aluminum.

(5) A sol comprising a solvent and 0.5 to 30% by weight of the poroussubstance set forth in any one of items (1) to (4) contained in thesolvent.

(6) A porous substance sol comprising inorganic particles which areamorphous and have uniform pores and which are produced by a processcomprising the steps of:

-   -   mixing a metal source comprising a metal oxide and/or a        precursor thereof, a template, and water to prepare a metal        oxide/template composite sol; and    -   removing the template from the composite.

(7) The porous substance sol set forth in item (6), wherein the processfurther comprises the step of adding an alkali aluminate.

(8) The porous substance sol set forth in item (6) or (7),

-   -   wherein the template is a nonionic surface active agent        represented by structural formula (1):        HO(C₂H₄₀)_(a)—(C₃H₆O)_(b)—(C₂H₄O)_(c)H  (1)        wherein a and c each represent 10 to 110; and b represents 30 to        70, and    -   wherein the metal source, template and water are mixed at a        water to template (water/template) weight ratio ranging from 10        to 1000.

(9) The porous substance sol set forth in any one of items (6) to (8),wherein the metal source and the template are mixed at a pH ranging from3 to 12.

(10) The porous substance sol set forth in any one of items (6) to (9),wherein the metal source is active silica.

(11) The porous substance sol set forth in item (10), wherein the metalsource, template and water are mixed at a weight ratio of the templateto the active silica as the metal source in terms of SiO₂(template/SiO₂) ranging from 0.01 to 30.

(12) A porous substance obtained from the porous substance sol set forthin any one of items (6) to (11).

(13) An inkjet recording medium comprising a support and one or more inkabsorbing layers provided on the support,

-   -   wherein at least one of the ink absorbing layer(s) contains the        porous substance set forth in any one of items (1) to (4) and        (12).

(14) A coating liquid for an inkjet recording medium containing theporous substance and/or the porous substance sol set forth in any one ofitems (1) to (12).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pore size distribution diagram of the porous substancesynthesized in Example 1.

FIG. 2 is a powder X-ray diffraction pattern of the porous substancesynthesized in Example 1.

FIG. 3 is a TEM photograph of the porous substance synthesized inExample 2.

FIG. 4 is a pore size distribution diagram of the porous substancesynthesized in Example 4.

FIG. 5 is a powder X-ray diffraction pattern of the porous substancesynthesized in Example 4.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail.

The present invention provides a porous amorphous inorganic substancewith uniform pores which has an average particle size, D_(L), of 10 to400 nm as measured by a dynamic light scattering method and a specificsurface area difference, S_(B)-S_(L), between a conversion specificsurface area S_(L) calculated from D_(L) and a nitrogen gas adsorptionspecific surface area of the particles S_(B) obtained by the BET method,of 250 m²/g or more.

The term “amorphous” as used herein means that the porous substanceshows no regularity over a long range (i.e., no long-period order) inits atomic structure or pore structure nor a distinct peak in powderX-ray diffractometry. For example, an amorphous substance shows aregularity only in as short a range as few nanometers referring to itsatomic arrangement, or only in as short a range as 10 pores at the mostreferring to its pore arrangement.

The term “porous” as used herein means having pores that are measurableby the nitrogen adsorption method and preferably having a pore volume of0.1 ml/g or larger, more preferably 0.5 ml/g or larger. The average poresize of the porous substance is preferably, but not limited to, 6 nm orgreater, more preferably 6 to 30 nm. While dependent on use, larger poresizes are preferred for allowing a larger substance to enter the poreswith ease and to diffuse more rapidly. Small pore sizes are notfavorable because water vapor, etc. in air can clog the pores to hindera substance from flowing into the pores. The phrase “having a uniformpore size” means that 50% or more of the pores based on the total porevolume (total volume of pores having diameters of 50 nm or smaller whichare measurable by the nitrogen adsorption method) falls within a porediameter range of ±50% of the average pore size in the relationshipbetween the pore size and the total pore volume determined from thenitrogen adsorption isothermal curve. Whether or not the pores areuniform can also be confirmed through TEM observation.

The average particle size of the porous substance according to thepresent invention as measured by a dynamic light scattering method ispreferably 1 to 400 nm, more preferably 1 to 300 nm, particularlypreferably 10 to 200 nm. If the porous substance has a particle size of200 nm or smaller when dispersed in a solvent or a binder, furtherhigher transparency can be obtained. Particularly, when used as an inkabsorbing layer of an inkjet recording medium, printed matter with goodcolor development and high color density can be obtained owing to thehigh transparency. Particles greater than 200 nm result in reducedtransparency, and particles greater than 400 nm easily settle out inhigh concentration sols, which are unfavorable for some uses.

Assuming that the porous substance particles are spherical, theconversion specific surface area S_(L) (m²/g) is calculated from theaverage particle size D_(L) (mn) measured by a dynamic light scatteringmethod according to equation: S_(L)=6×10³/(density (g/cm³)×D_(L)).Having a difference between this value and a nitrogen adsorptionspecific surface area SB obtained by the BET method, i.e., S_(B)-S_(L),of 250 m²/g or more means that the particles of the porous substance areextremely porous. A porous substance having a small S_(B)-S_(L)difference exhibits reduced capability to absorb a substance, forexample, reduced ink absorptivity when used as an ink absorbing layer.The S_(B)-S_(L) value is preferably 1500 m²/g or smaller. When the valueis high, it may result in deteriorated handling properties.

The term “sol” as used herein denotes a colloid solution comprising aliquid as a dispersion medium and the porous substance of the inventionas a dispersoid. Any dispersion medium can be used so long as it doesnot cause sedimentation. Preferably, water, an alcohol, or a mixedsolvent of water and an alcohol is used. Suitable alcohols include loweralcohols, such as ethanol and methanol. The dispersion medium maycontain an alkali such as NaOH, a low-molecular polyvinyl alcohol(hereinafter referred to as low-molecular PVA) and a surface activeagent as stabilizers for preventing particles from agglomeration. Thesol concentration is preferably 0.5 to 30% by weight, more preferably 5to 30% by weight, though it varies depending on the use. Sols having toolow concentrations are disadvantageous not only from the standpoint ofeconomy and transportation but also in that they hardly dry when usedfor coating. Too high concentrations result in high viscosity, whichpossibly leads to a deteriorated stability unfavorably.

The metal source which can be used in the invention is a metal oxideand/or a precursor thereof. Species of the metal include silicon;alkaline earth metals in the Group 2 elements such as magnesium andcalcium; aluminum, gallium and rare earth elements in the Group 3elements; titanium and zirconium in the Group 4 elements; phosphorus andvanadium in the Group 5 elements; manganese and tellurium in the Group 7elements; and iron and cobalt in the Group 8 elements. The precursorincludes inorganic salts, such as nitrates and hydrochlorides, organicacid salts, such as acetates and naphthenates, organometallic salts(e.g., alkylaluminum), alkoxides and hydroxides of these metals. Theprecursor is not limited to these examples, and any metal oxideprecursor that can be synthesized by the synthesis methods describedbelow can be employed. These metal oxides and their precursors can beused either individually or as a combination of two or more thereof.

In the case of using silicon as a metal species, the precursor includesone capable of finally becoming silica through repetition ofcondensation or polymerization. Preferably alkoxides, such astetraethoxysilane, methyltriethoxysilane, dimethyltriethoxysilane and1,2-bis(triethoxysilyl)ethane, and active silica are used alone or incombination of two or more thereof. Active silica is especiallypreferred for its inexpensiveness and high safety. Active silica for usein the invention can be prepared by, for example, extraction from waterglass with an organic solvent or ion-exchange of water glass. Where itis prepared by bringing water glass into contact with an H⁺ cationexchanger, it is preferred for industrial production to use No. 3 waterglass because of its low Na content and low price. Preferred examples ofthe cation exchanger include, but are not limited to, sulfonatedpolystyrene divinylbenzene-based strongly acidic ion exchange resins(e.g., Amberlite IR-120B from Rohm & Haas).

The template for use in the present invention is not limited andincludes cationic (such as quaternary ammonium type surfactants),anionic, nonionic or amphoteric surface active agents, and neutraltemplates such as amines, e.g., dodecylamine, tetradecylamine,hexadecylamine and octadecylamine, and amine oxides. It is preferred touse nonionic surface active agents, such as triblock agents (e.g., AdekaPluronic L•P•F•R series from Asahi Denka Kogyo K.K.), polyethyleneglycols (e.g., Adeka PEG series from Asahi Denka), andethylenediamine-based agents (e.g., Adeka Pluronic TR series).

The nonionic surface active agents include triblock agents comprisingethylene oxide and propylene oxide, especially those represented bystructural formula: HO(C₂H₄₀)_(a)—(C₃H₆O)_(b)—(C₂H₄₀)_(c)H, wherein aand c each represent 10 to 110; and b represents 30 to 70, and compoundsrepresented by structural formula: R(OCH₂CH₂)_(n)OH, wherein Rrepresents an alkyl group having 12 to 20 carbon atoms; and n represents2 to 30. Examples thereof are Pluronic P103(HO(C₂H₄O)₁₇—(C₃H₆O)₆₀—(C₂H₄O)₁₇H) P123(HO(C₂H₄O)₇₀—(C₃H₆O)₇₀—(C₂H₄O)₂₀H) and P85, each available from AsahiDenka, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, andpolyoxyethylene stearyl ether.

In order to vary the pore size, an organic assistant, such as anaromatic hydrocarbon having 6 to 20 carbon atoms, an alicyclichydrocarbon having 5 to 20 carbon atoms, an aliphatic hydrocarbon having3 to 16 carbon atoms, and amine or halogen derivatives thereof, such astoluene, trimethylbenzene, and triisopropylbenzene, may be added.

The process according to the present invention is described below.

The reaction between the metal source and the template can be carriedout, for example, after mixing and stirring a solution or dispersion ofthe metal source in a solvent and a solution or dispersion of thetemplate in a solvent, but is not limited thereto. The solvents includewater and a mixed solvent of water and an organic solvent. Alcohols arepreferred as the organic solvents. Preferred alcohols include loweralcohols, such as ethanol and methanol.

The composition of the reaction system, which varies depending on thetemplate, metal source and solvent, should be selected from such rangesthat do not cause particles to agglomerate or settle out and to enlargethe particle size. In order to prevent the particles' agglomeration orsedimentation, a stabilizer, such as an alkali (e.g., NaOH) and alow-molecular PVA, may be added.

In the case of using active silica as a metal source, Pluronic P103(from Asahi Denka) as a template, and water as a solvent, for example,the following composition can be used. A preferred P103/SiO₂ weightratio ranges 0.01 to 30, more preferably 0.1 to 5. A preferred organicassistant/P103 weight ratio is 0.02 to 100, more preferably 0.05 to 35.The water/P103 weight ratio during the reaction is preferably 10 to1000, more preferably 20 to 500. NaOH may be added as a stabilizer at anNaOH/SiO₂ weight ratio of 1×10⁻⁴ to 0.15. In the case of using PluronicP123, similar compositions can be used.

Mixing of the metal source, template and solvent is effected whilestirring preferably at 0 to 80° C., more preferably at 0 to 40° C.

The reaction proceeds easily at ambient temperature or, if necessary,under heating up to 100° C. Hydrothermal reaction conditions attemperatures as high as exceeding 100° C. are not necessary. Thereaction time ranges from 0.5 to 100 hours, preferably 3 to 50 hours.The pH during the reaction is preferably 3 to 12, more preferably 4 to12, particularly preferably 4 to 10. An alkali, e.g., NaOH or ammonia,or an acid, e.g., hydrochloric acid, acetic acid or sulfuric acid, maybe added for pH adjustment.

In producing a porous substance sol, an alkali aluminate can be addedeither before or after the formation of the composite or after removalof the template.

Where the composite contains silicon, addition of an alkali aluminateresults in production of a sol which is stable enough to withstandlong-term storage even when rendered acidic or having a cationicsubstance added.

The alkali aluminate which can be used includes sodium aluminate,potassium aluminate, lithium aluminate, ammonium primary aluminate, andguanidine aluminate, with sodium aluminate being preferred. The Na/Alelemental ratio in sodium aluminate is preferably 1.0 to 3.0.

The following description is made as an example referring to the casewhere an alkali aluminate solution is added after the removal of atemplate. An alkali aluminate solution is added while stirring at 0 to80° C., preferably 5 to 40° C. The concentration of the alkali aluminateto be added is preferably, but not limited to, 0.5 to 40% by weight,more preferably 1 to 20% by weight. The amount to be added, in terms ofAl/(Si+Al) elemental ratio where a porous substance sol containssilicon, is preferably 0.003 to 0.1, more preferably 0.005 to 0.05.After the addition, the reaction mixture is preferably heated at 40 to95° C., more preferably 60 to 80° C.

Next, the method for removing the template is described. For example, asolvent, e.g., an alcohol, is added to the resulting reaction solutionso as to remove the template from the composite, thus obtaining a poroussubstance. An ultrafiltration apparatus is used to advantage so that theporous substance can be handled as a sol. The membrane forultrafiltration can be of polysulfone, polyacrylonitrile, cellulose,etc. and in any of hollow fiber, flat sheet, spiral wound, and otherconfigurations. In order to prevent the particles from agglomerating, astabilizer such as an alkali (e.g., NaOH) or a low-molecular PVA may beadded. The solvent used for the template removal is not limited as longas it is capable of dissolving the template. Water that is easy tohandle or alcohols having high dissolving power are preferred. Thealcohols preferably include lower alcohols, such as methanol andethanol. While varying depending on the solvent used and the template,the temperature for the removal is preferably 0 to 80° C., morepreferably 20 to 80° C. The template thus removed can be reused aftersolvent removal. Alternatively, the porous substance may be obtained bycollecting the resulting composite by filtration or a like operation,washing with water, and drying, followed by contacting the driedcomposite with a supercritical fluid or a solvent (e.g., an alcohol) orcalcination to remove the template. The calcination is at or above thetemperature at which the template disappears, usually 500° C. or higher.The calcination time, though decided appropriately in connection withthe temperature, is about from 30 minutes to 6 hours. As further othermethods, the template can be removed by mixing and stirring thecomposite with a solvent or passing a solvent through a column, etc.packed with the composite.

For removing the solvent from the sol to give a porous substance,methods of heat drying, vacuum drying, spray drying, or supercriticaldrying can be employed.

Various modifications can be added to the porous substance and/or theporous substance sol of the present invention depending on theirintended use. For example, a surface modification with a silane couplingagent, etc. may be made, or a metal, such as platinum or palladium, maybe supported thereon.

Having pores, the porous substance of the invention is expected to havesuch functions as absorbing a substance therein, embracing andprotecting a substance, or slowly releasing a substance. It can be usedas, for example, an adsorbent of an adsorption heat pump, a humiditymodifier, a catalyst, a catalyst carrier, an ink absorber, a medicalcarrier used in a drug delivery system and the like, and a carrier forcosmetics, foods, and dyes. Being finely particulate, the poroussubstance of the invention is also applicable to those fields requiringtransparency, smoothness, and the like. For instance, it can be used asa filler of rubbers, resins or paper, a thickener of coatings, athixotropic agent, an anti-settling agent, and an antiblocking agent forfilms. Having transparency, pores and a low density, the poroussubstance of the invention can also be used as a low-refractive indexfilm, an antireflection film, a low-dielectric film, a hard coat film, aheat insulator, a sound absorber, and so forth. In particular, takingadvantages of the abilities to form a smooth transparent film and toabsorb a substance, the porous substance can be suitably used inphotograph-like inkjet recording media.

Application to inkjet recording media is hereinafter described. Inkjetinks to be used can contain either dyes or pigments as a colorant and beeither aqueous or non-aqueous.

The inkjet recording medium according to the present invention comprisesa support and at least one ink absorbing layer provided on the support.If desired, two or more ink absorbing layers are provided. The provisionof multi-layered ink absorbing layers make it possible to distributefunctions each layer, for example, imparting a gloss to the surface. Atleast one of the ink absorbing layers contains the porous substance ofthe invention.

The content of the porous substance of the invention is preferably, butnot limited to, 10 to 99% by weight based on the ink absorbing layer inwhich the porous substance is incorporated, and 1 to 99% by weight basedon the total weight of the ink absorbing layers. Low porous substancecontents unfavorably result in reduced ink absorptivity.

The ink absorbing layer can contain an organic binder as a binder thatdoes not spoil the ink absorbing properties of the porous substance.Useful organic binders include polyvinyl alcohol (PVA) and derivativesthereof, polyvinyl acetates, polyvinylpyrrolidones, polyacetals,polyurethanes, polyvinylbutyrals, poly(meth)acrylic acids (or esters),polyamides, polyacrylamides, polyester resins, urea resins, melamineresins; those originated in natural polymers, such as starch and starchderivatives, cellulose derivatives, e.g., carboxymethyl cellulose andhydroxyethyl, casein, and gelatin; latices, and emulsions. The laticesinclude vinyl acetate polymer latices, styrene-isoprene copolymerlatices, styrene-butadiene copolymer latices, methylmethacrylate-butadiene copolymer latices, acrylic ester copolymerlatices, and functional group-modified polymer latices obtained bymodifying these copolymers with a functional group-containing (e.g., acarboxyl-containing) monomer. The PVA derivatives includecation-modified polyvinyl alcohol and silanol-modified polyvinylalcohol. These binders can be used in combination.

The organic binder content is not particularly limited. Polyvinylalcohol, for example, is preferably used in an amount of 5 to 400 partsby weight, particularly preferably 5 to 100 parts by weight, per 100parts by weight of the porous substance. Larger amounts lead to reducedfilm-forming properties, and smaller amounts lead to reduced inkabsorptivity, each of which is thus unfavorable.

The present invention also provides a coating liquid for inkjetrecording media which comprises components for forming an ink absorbinglayer and a solvent. The solvent to be used preferably includes, but isnot limited to, water-soluble solvents, such as alcohols, ketones, andesters, and/or water. If desired, the coating liquid can contain pigmentdispersants, thickeners, flowability modifiers, defoaming agents, foaminhibitors, parting agents, foaming agents, colorants, and the like.

It is preferred that at least one ink absorbing layer contain a cationicpolymer. The cationic polymer contained improve water resistance of aprinted image. While any cationic polymer is usable as long as it iscationic, it is preferable to use one containing at least one of primaryamine, secondary amine or tertiary amine substituents and their saltsand quaternary ammonium salt substituents. Examples therefor include adimethyldiallylammonium chloride polymer, a dimethyldiallylammoniumchloride-acrylamide copolymer, an alkylamine polymer, a polyaminedicyanpolymer, and polyallylamine hydrochloride. Preferred weight averagemolecular weights of the cationic polymers are, but not limited to,1,000 to 200,000.

It is preferred for at least one ink absorbing layer to contain anultraviolet absorber, a hindered amine light stabilizer, a single oxygenquencher or an antioxidant. These substances, if contained, improvelight fastness of a printed image. Preferably used ultraviolet absorbersinclude, but are not limited to, benzotriazole compounds, benzophenonecompounds, titanium oxide, cerium oxide, and zinc oxide. Preferably usedhindered amine light stabilizers include, but are not limited to, thosehaving a piperidine ring containing an N—R moiety (wherein R is ahydrogen atom, an alkyl group, a benzyl group, an allyl group, an acetylgroup, an alkoxy group, a cyclohexyl group or a benzyloxy group).Preferably used single oxygen quenchers include, but are not limited to,aniline derivatives, organonickel compounds, spiro-chroman compounds,and spiro-indane compounds. Preferably used antioxidants include, butare not limited to, phenol compounds, hydroquinone compounds,organosulfur compounds, phosphorus compounds, and amine compounds.

It is preferred for at least one ink absorbing layer to contain analkaline earth metal compound. The alkaline earth metal compound, ifcontained, improves light fastness. Preferably used alkaline earth metalcompounds include oxides, halides, and hydroxides of magnesium, calciumor barium. The method for incorporating the alkaline earth metalcompound into the ink absorbing layer is not particularly restricted. Itcan be added to a coating slurry or added or adhered to the inorganicporous substance during or after the synthesis. The amount of thealkaline earth metal compound is preferably 0.5 to 20 parts by weight interms of an oxide per 100 parts by weight of the inorganic poroussubstance.

It is preferred for at least one ink absorbing layer to contain anonionic surface active agent. The nonionic surface active agent, ifcontained, improves image quality and light fastness. Preferably usednonionic surface active agents include, but are not limited to, higheralcohols, ethylene oxide adducts of carboxylic acids, and ethyleneoxide-propylene oxide copolymers, with ethylene oxide-propylene oxidecopolymers being more preferred. The method of incorporating thenonionic surface active agent into the ink absorbing layer is notparticularly restricted. It can be added to a coating slurry or added oradhered to the inorganic porous substance during or after the synthesis.

It is preferred for at least one ink absorbing layer to contain analcohol compound. The alcohol compound, if contained, improves imagequality and light fastness. Preferably used alcohol compounds include,but are not limited to, aliphatic alcohols, aromatic alcohols,polyhydric alcohols, and hydroxyl-containing oligomers, with polyhydricalcohols being more preferred. The method of incorporating the alcoholcompound into the ink absorbing layer is not particularly restricted. Itcan be added to a coating liquid slurry or added or adhered to theporous inorganic substance during or after the synthesis.

It is preferred for at least one ink absorbing layer to contain aluminahydrate. The alumina hydrate, if contained, improves image quality andwater resistance. The structure of alumina hydrate to be used includes,but is not limited to, a boehmite structure, a psuedoboehmite structure,and an amorphous structure. Alumina hydrate of pseudoboehimite structureis preferred.

It is preferred for at least one ink absorbing layer to containcolloidal silica and/or dry process silica. The colloidal silica and/ordry process silica, if contained, improve image quality and impartgloss. Colloidal silica that can be used is not particularly limited,and ordinary anionic colloidal silica or cationic colloidal silicaobtainable by, for example, reaction with a polyvalent metal compound,e.g., aluminum ions can be used. The dry process silica includes, but isnot limited to, fumed silica synthesized by burning silicontetrachloride in a hydrogen oxygen flame.

The dry process silica can be used as it is or as having its surfacemodified with a silane coupling agent, etc.

In the present invention, a gloss layer can be provided as an outermostlayer. The means for providing a gloss layer includes, but is notlimited to, a method in which ultrafine particles such as colloidalsilica and/or dry process silica are incorporated, a supercalenderingmethod, a gloss calendering method, and a casting method.

The support which can be used in the invention preferably includes, butis not limited to, paper, polymer sheets, polymer films, and fabrics. Ifdesired, the support can be subjected to a surface treatment, such as acorona discharge treatment. The thickness of the ink absorbing layer isnot particularly limited but preferably in a range of 1 to 100 μm, andthe coating weight is preferably 1 to 100 g/m². Methods for applying thecoating liquid are not particularly limited, and a blade coater, an airknife coater, a roll coater, a brush coater, a curtain coater, a barcoater, a gravure coater, a spray, etc. can be used.

EXAMPLES

The present invention will now be illustrated in greater detail withreference to the following Examples.

Powder X-ray diffraction patterns were obtained by measurement with RINT2500, supplied by Rigaku Corp.

Pore size distributions and specific surface areas were measured withAutosorb-1, supplied from Quantachrome, by using nitrogen. The pore sizedistributions were calculated according to the BJH method. Average porediameters were calculated from the peak value in the mesopore region ofthe differential pore size distribution curve obtained by the BJHmethod.

The average particle size by a dynamic light scattering method wasmeasured with a laser zeta potentiometer ELS-800 supplied by OtsukaElectronics Co., Ltd.

TEM photographs were taken with a TEM H-7100 from Hitachi, Ltd.

A test on stability in an acidic region was carried out as follows.

A cation exchange resin in an H⁺ form (Amberlite IR-120B) was dispersedin a prepared porous substance sol and thoroughly stirred to make thesol acidic. After the cation exchange resin was separated by filtration,the sol was put into a glass screw tube, sealed not to evaporate, andallowed to stand at 25° C. The sol was observed to see whether gelationoccurred immediately after the acidification, after 3 hours and afterone months from the acidification. Samples suffering from gelation wererated “bad”, and those showing no change “good”.

Transparency of an applied coating film was evaluated as follows. Acoating liquid consisting of a porous substance, PVA 203 (available fromKuraray Co., Ltd.), and PVA 235 (from Kuraray) at a solid basis ratio of100:1:30 was applied to a transparent PET film (Lumirror Q80D, fromToray Industries, Inc.) to a dry coating thickness of 20 μm. Thetransparency of the coating film was measured with D-300 (from NipponDenko Co., Ltd.) and evaluated in terms of haze value taking the haze ofthe transparent PET as a standard.

For print performance evaluation, the coating film was printed solidwith each of yellow, magenta, cyan and black inks using a commerciallyavailable inkjet printer PM-800C, supplied from Seiko Epson Corp. Inkabsorptivity of the coating film was rated “good”, “fairly good” or“bad”, judging from blurring after printing and the degree of inktransfer to white paper pressed on the printed area immediately afterthe printing.

EXAMPLE 1

In 100 g of water was dispersed 100 g of a cation exchange resin havingbeen converted into an H⁺ form (Amberlite IR-120B). A solution of 33.3 gof No. 3 water glass (SiO₂: 29 wt %; Na₂O: 9.5 wt %) in 66.7 g of waterwas added to the dispersion, followed by stirring well. The cationexchange resin was removed by filtration to give 200 g of an activesilica aqueous solution, which was found to have an SiO₂ concentrationof 5.0 wt %. In 1360 g of water was dissolved 5 g of Pluronic P103 fromAsahi Denka, and 60 g of the active silica aqueous solution was addedthereto while stirring in a 35° C. water bath. To the mixture wasfurther added 20 ml of a 0.015 mol/l NaOH aqueous solution. Theresulting mixture had a pH of 7.5, a water/P103 weight ratio of 289.1,and a P103/SiO₂ weight ratio of 1.67. The mixture was stirred at 35° C.for 15 minutes and then allowed to stand and to react at 80° C. for 24hours. The nonionic surface active agent was removed from the resultingsolution by means of an ultrafiltration apparatus to give a transparentporous substance sol having an SiO₂ concentration of about 4 wt %. Thesample in the solution had an average particle size of 60 nm as measuredby a dynamic light scattering method and a conversion specific surfacearea of 45 m²/g. Table 1 shows the results of evaluations on a coatingfilm prepared by using the resulting porous substance sol.

The sol was dried at 105° C. to give a porous substance. The X-raydiffraction pattern of the resulting sample showed no distinct peaks.The sample had an average pore diameter of 8 nm, a pore volume of 1.21ml/g, and a BET nitrogen adsorption specific surface area of 720 m²/g,giving a difference of 675 m²/g from the conversion specific surfacearea.

EXAMPLE 2

Synthesis was carried out in the same manner as in Example 1, except forreplacing P103 with P123 and changing the reaction temperature from 80°C. to 90° C., to obtain a transparent porous substance sol having anSiO₂ concentration of about 6.9 wt %. The sample in the resultingsolution had an average particle size of 130 nm as measured by a dynamiclight scattering method and a conversion specific surface area of 21m²/g. A specimen for TEM was prepared from the solution by means of anebulizer and observed under a TEM (FIG. 3). Fine pores with uniformsize were observed, and it can be seen that there is no long-periodorder. The sol was dried at 105° C. to obtain a porous substance. TheX-ray diffraction pattern of the sample showed no distinct peaks. Thesample had an average pore diameter of 9 nm and a pore volume of 1.81ml/g. The BET nitrogen adsorption specific surface area was 690 m²/g,showing a difference of 670 m²/g from the conversion specific surfacearea.

The results of evaluation on a coating film prepared by using theresulting porous substance sol are shown in Table 1.

EXAMPLE 3

In 600 g of water was dispersed 600 g of a cation exchange resin havingbeen converted into an H⁺ form (Amberlite IR-120B). A solution of 200 gof No. 3 water glass (SiO₂: 30 wt %; Na₂O: 9.5 wt %) in 400 g of waterwas added to the dispersion, followed by stirring well. The cationexchange resin was removed by filtration to give 1200 g of an activesilica aqueous solution, which had an SiO₂ concentration of 5.0 wt %.The solution was diluted with 3800 g of purified water.

In 900 g of water was dissolved 100 g of Pluronic P123 from Asahi Denka,and 6000 g of the diluted active silica aqueous solution was addedthereto while stirring at room temperature. The resulting mixture had apH of 3.7, a water/P123 weight ratio of 58.4, and a P123/SiO₂ weightratio of 1.67. The mixture was allowed to stand to react at 95° C. for24 hours. The nonionic surface active agent was removed from theresulting solution by means of an ultrafiltration apparatus to give atransparent porous substance sol having an SiO₂ concentration of about5.2 wt %. The sample in the solution had an average particle size of 350nm as measured by a dynamic light scattering method and a conversionspecific surface area of 8 m²/g. Table 1 shows the results ofevaluations on a coating film prepared by using the resulting poroussubstance sol.

The sol was dried at 105° C. to give a porous substance. The X-raydiffraction pattern of the resulting sample showed no distinct peaks.The sample had an average pore diameter of 9 nm, a pore volume of 2.37ml/g, and a BET nitrogen adsorption specific surface area of 590 m²/g,giving a difference of 582 m²/g from the conversion specific surfacearea.

EXAMPLE 4

In 300 g of water was dispersed 300 g of a cation exchange resin havingbeen converted into an H⁺ form (Amberlite IR-120B). A solution of 100 gof No. 3 water glass (SiO₂: 30 wt %; Na₂O: 9.5 wt %) in 200 g of waterwas added to the dispersion, followed by stirring well. The cationexchange resin was removed by filtration to give 600 g of an activesilica aqueous solution, which had an SiO₂ concentration of 5.0 wt %.The solution was diluted with 1675 g of purified water. Separately, 500g of an aqueous solution having dissolved therein 50 g of Pluronic P123,200 g of a 0.015 mol/l sodium hydroxide aqueous solution, and 25 g oftrimethylbenzene were mixed and stirred under heating at 60° C. for 1hour to prepare a white transparent solution. The resulting solution wasadded dropwise to the diluted active silica aqueous solution, and themixture was heated at 80° C. for 24 hours. P123 was removed from theresulting solution in an ultrafiltration apparatus to give a poroussubstance sol having an SiO₂ concentration of about 7.5 wt %(hereinafter referred to as liquid A). A 1 wt % aqueous solution ofsodium aluminate was added to liquid A to result in an Al/(Si+Al)elemental ratio of 0.01. The mixture was heated at 80° C. for 24 hoursto give a porous substance sol (hereinafter referred to as liquid B).

The sample in the solution had an average particle size of 195 nm asmeasured by a dynamic light scattering method and a conversion specificsurface area of 15 m²/g. The solution was dried at 105° C. to give aporous substance. The X-ray diffraction pattern of the resulting sampleshowed no distinct peaks. The sample had an average pore diameter of 18nm, a pore volume of 1.67 ml/g, and a BET nitrogen adsorption specificsurface area of 413 m²/g, giving a difference of 398 m²/g from theconversion specific surface area.

Liquid A and liquid B were subjected to the stability test. The resultsobtained are summarized in Table 2.

EXAMPLE 5

A 10 wt % aqueous solution of sodium aluminate was added to solution Aobtained in Example 4 to result in an Al/(Si+Al) elemental ratio of 0.1.The resulting mixture was heated at 80° C. for 24 hours to obtain aporous substance sol. The results of a stability test on the sol areshown in Table 2.

EXAMPLE 6

To 18.4 g of liquid A prepared in Example 4 was added 1.9 g of a 1 wt %aqueous solution of sodium aluminate to result in an Al/(Si+Al)elemental ratio of 0.01. The resulting mixture was left to stand at roomtemperature for 24 hours to obtain a porous substance sol. The resultsof a stability test on the sol are shown in Table 2.

COMPARATIVE EXAMPLE 1

The addition of a 0.015 mol/l NaOH aqueous solution in Example 1 wasreplaced with addition of 140 ml of a 0.1 mol/l HCl aqueous solution.Whereupon a white precipitate was formed. The resultant mixture had a pHof 0.96. The mixture was left to stand to react at 80° C. for 24 hours.The composite thus formed was collected by filtration, washed withwater, and dried at 105° C. The composite was fired in air at 550° C.for 6 hours. The resulting sample had too large particle sizes to bemeasured by a dynamic light scattering method. A coating film formed ofthe resulting substance was white opaque, the haze of which was outsidea measurable range.

COMPARATIVE EXAMPLE 2

The addition of the active silica aqueous solution in Example 1 wasreplaced with addition of a solution of 10 g of No. 3 water glass (SiO₂:30 wt %; Na₂O: 9.5 wt %) in 50 g of water. Further, the addition of the0.015 mol/l NaOH aqueous solution in Example 1 was replaced withaddition of 31 ml of a 0.1 mol/l HCl aqueous solution to adjust themixture to pH 6.1, whereupon a gel precipitate was formed. The mixturewas left to stand to react at 80° C. for 24 hours. The composite thusformed was collected by filtration, washed with water, and dried at 105°C. The composite was fired in air at 550° C. for 6 hours. The sample hadtoo large particle sizes to be measured by a dynamic light scatteringmethod. A coating film formed of the resulting substance was whiteopaque, the haze of which was outside a measurable range.

COMPARATIVE EXAMPLE 3

In 30 g of water was dissolved 10 g of Pluronic P103 from Asahi Denka.Fifty grams of an active silica aqueous solution having an SiO₂concentration of 5 wt %, which was prepared in the same manner as inExample 1, was added thereto while stirring in a 35° C. water bath. Tothe mixture was further added 2.5 ml of a 0.1 mol/l NaOH aqueoussolution, whereupon a white precipitate was formed. The mixture had a pHof 7.0. The water/P103 weight ratio was 8, and the P103/SiO₂ weightratio was 4. The mixture was left to stand to react at 80° C. for 24hours. The resulting composite was collected by filtration, washed withwater, and dried at 105° C. The composite was fired in air at 550° C.for 6 hours. The sample had too large particle sizes to be measured by adynamic light scattering method. A coating film formed of the resultingsubstance was white opaque, the haze of which was outside a measurablerange.

COMPARATIVE EXAMPLE 4

A commercially available colloidal silica solution (Snowtex PS-M,available from Nissan Chemical Industries, Ltd.) had an average particlesize of 150 nm as measured by a dynamic light scattering method and aconversion specific surface area of 18 m²/g. The results of evaluationson a coating film formed of the solution are shown in Table 1.

The solution was dried at 105° C. The X-ray diffraction pattern of thesample showed no distinct peaks. The BET nitrogen adsorption specificsurface area of the sample was 100 m²/g, giving a difference of 82 m²/gfrom the conversion specific surface area. TABLE 1 Transparency InkAbsorbtivity Example 1 3 fairly good Example 2 5 good Example 3 20 goodExample 4 1 good Comparative 4 bad Example 4

TABLE 2 Immediately after After After 1 pH Acidification 3 hrs monthExample 4 3.2 bad (gelled) — — (liquid A) Example 4 3.24 good (stable)goo good (liquid B) (stable) (stable) Example 5 3.18 good (stable) goodgood (stable) (stable) Example 6 3.14 good (stable) bad — (gelled)

INDUSTRIAL APPLICABILITY

Having pores and being finely particulate, the porous substance of thepresent invention is expected to have such effects as absorbing asubstance, embracing and protecting a substance, or slowly releasing asubstance and is also applicable to those fields further requiringtransparency, smoothness, and the like. Being amorphous, it shows nosuch shape selectivity as is observed with a substance having a regularstructure.

Where the porous substance of the invention contains silicon, additionof an alkali aluminate in the production thereof yields a sol which isstable enough to withstand long-term storage even when rendered acidicor having a cationic substance added thereto.

The inkjet recording medium according to the present invention givesexcellent effects in ink absorptivity and transparency.

1. A porous substance sol comprising inorganic particles which are amorphous and have uniform pores and which are produced by a process comprising the steps of: mixing a metal source comprising a metal oxide and/or a precursor thereof, a template, and water to prepare a metal oxide/template composite sol; and removing the template from the composite.
 2. The porous substance sol according to claim 1, wherein said process further comprises the step of adding an alkali aluminate.
 3. The porous substance sol according to claim 1 or 2, wherein said template is a nonionic surface active agent represented by structural formula (1): HO(C₂H₄O)_(a)—(C₃H₆O)_(b)—(C₂H₄O)_(c)H  (1) wherein a and c each represent 10 to 110; and b represents 30 to 70, and wherein said metal source, template and water are mixed at a water to template (water/template) weight ratio ranging from 10 to
 1000. 4. The porous substance sol according to claim 1 or 2, wherein said metal source and said template are mixed at a pH ranging from 3 to
 12. 5. The porous substance sol according to claim 1 or 2, wherein said metal source is active silica.
 6. The porous substance sol according to claim 5, wherein said metal source, template and water are mixed at a weight ratio of said template to said active silica as the metal source in terms of SiO₂, template/SiO₂, ranging from 0.01 to
 30. 7. A porous substance obtained from a porous substance sol according to claim 1 or
 2. 8. An inkjet recording medium comprising a support and one or more ink absorbing layers provided on the support, wherein at least one of said ink absorbing layer(s) contains a porous substance according to claim
 7. 9. A coating liquid for an inkjet recording medium containing a porous substance sol according to claim
 1. 10. A coating liquid for an inkjet recording medium containing a porous substance according to claim
 7. 